1. Field of the Invention
The invention relates to a process for manufacturing an article in slab form and more precisely to an article comprising a hydrated matrix which contains cement and sand and is reinforced by fibres.
2. Description of the Related Art
The invention will be more particularly described for the manufacture of building covering elements, such as building roofing slabs imitating slate. However, the invention is not limited to this type of article and should be interpreted in a non-limiting way and as encompassing any type of article comprising a hydrated matrix which contains cement and sand and is reinforced by fibres.
It has already been proposed in European Patent Application Serial No. 165,388 to produce building roofing slabs imitating slate. It turns out that the articles obtained in accordance with the teaching of this document have a relatively high relative density (greater than 2) and are brittle. This brittleness prevents them from being produced with a small thickness without the risk of fracturing or cracking. The articles thus obtained are therefore unsuitable for forming roofing slabs.
The subject of the invention is thus a manufacturing process resulting in the production of thin slabs which may be conveniently used for building coverings, especially as roofing, and have the appearance of slate.
The French Patent Application Serial No. 93/15184 of the Applicant has already proposed such a manufacturing process. The process described according to this document includes in particular a rolling step which has two functions. First of all, this step confers the desired thickness on the articles produced. The second function of the rolling is to improve the orientation of the reinforcing fibres with the aim of obtaining isotropic mechanical properties. Although the process proposed by this document leads to lighter articles with the desired thickness without thereby increasing their brittleness, it does, however, require working conditions which are not very satisfactory because the rolling, which is carried out by contact with a succession of rolls, may run the risk of the matrix sticking on the rolls. Apart from the risk of degrading the matrix and therefore of increasing the production costs because of the loss of material, it is necessary to clean the equipment very frequently. This maintenance also leads to an increase in the costs. Should the matrix stick on the rolls, the latter may in fact carry off material which hardens and modifies the appearance of the surface of the rolls. The rolling operations are then rendered ineffective. It is therefore necessary to provide frequent cleaning of the equipment, which cleaning decreases the production rates and increases the cost.